1. Place the chocolate and water in a bowl over a pan of gently simmering water and leave to slowly melt. Remove from the heat , stir and leave to cool for about 5 minutes.
2. Whip the cream until it thickens to form soft peaks and , in a separate bowl, whisk the egg white until it also forms soft peaks.
3. Pour the melted chocolate into the whipped cream and gently stir in. fold in the egg white before spooning into the coffee cups, making sure you leave about 1 cm of a rim at the top of the coffee.
4. Ideally chill in the fridge for about 2-3 hours to set, but they can be eaten straight away. Just before serving, pour over the warm liqueured espresso and enjoy straight away.